The present invention relates to a magnetic recording and reproducing device in which an optimum recording bias current, optimum recording level and optimum recording equalization characteristic are automatically set.
A magnetic recording and reproducing device in which an optimum recording bias current, optimum recording level and optimum recording equalization characteristic are automatically set is described, for example, in Japanese Patent Application No. 79/116,206 (OPI). To set the optimum recording bias current, a recording bias current is varied at arbitrary time intervals, reference recording/reproducing signals corresponding to the bias current thus varied are stored, a maximum value of the stored signals is detected, and the bias current is fixed at the value corresponding to the maximum reference recording/reproducing signal. To set the optimum recording level, a recording level of a signal in a low-frequency range is varied at arbitrary time intervals, reference recording/reproducing signals corresponding to the recording level thus varied are compared with a reference level, and the recording level is fixed at the value at which the level of the reference recording/reproducing signal is equal to that of the reference value. Finally, to set the optimum recording equalization characteristic, a recording equalization characteristic is varied at arbitrary time intervals, reference recording/reproducing signals corresponding to the recording equalization characteristic thus varied are compared with a reference level, and the recording equalization characteristic is fixed at the value at which the reference recording/reproducing signal equal to the reference level is obtained.
The construction of the magnetic recording and reproducing device described above is shown in FIG. 1. The operation of the device of FIG. 1 will be described in accordance with the flowchart shown in FIG. 2.
Under the control of a CPU (Central Processing Unit) 5, a bias current varying circuit 10 gradually increases a bias current supplied from a bias oscillation circuit 1 to a recording head 7. The CPU 5 also drives switches 15 and 14 to supply a signal of a low frequency, for example, a frequency of 333 Hz, produced by a low-frequency oscillator 2 through switches 15 and 14, a recording level varying circuit 12 and a recording equalizer varying circuit 11 to the recording head 7. A signal produced by superposing the bias current on the low-frequency signal is recorded on the magnetic tape by the recording head 7. The recorded signal is reproduced from the magnetic tape by a reproducing head 8. The level of the reproduced signal is detected by a reproduced level detecting circuit 4. The maximum value of the detected reproduced level is determined by the CPU 5, which in turn sets the bias current varying circuit 10 to output the optimum bias current of the value at which the maximum reproduced level is obtained. These operations are shown by steps a-d in the flowchart of FIG. 2.
Also under the control of the CPU 5, the recording level varying circuit 12 increases the amplitude of the low-frequency signal supplied to the recording head 7. The signal thus recorded on the magnetic tape is reproduced by the reproducing head 8. The level of the reproduced signal is then detected by the reproduced level detecting circuit 4. The CPU 5 sets the recording level varying circuit 12 to output the recording level at which the reproduced level detected by the reproduced level detecting circuit 4 becomes equal to a reference level. These operations are shown by steps e, f, and g in the flowchart of FIG. 2.
Finally, the switch 15 is driven by the CPU 5 to supply a high-frequency signal of 10 kHz produced by a high-frequency oscillator 3 to the recording equalizer circuit 11 through the recording level varying circuit 12. Also under the control of the CPU 5, the recording equalizer varying circuit 11 gradually increases the amplitude of the high-frequency signal of 10 kHz supplied to the recording head 7. The high-frequency signal thus recorded on the magnetic tape is reproduced by the reproducing head 8. The level of the reproduced signal is detected by the reproduced level detecting circuit 4. The CPU 5 finally sets the recording equalizer varying circuit 11 to output the high-frequency signal of the amplitude at which the reproduced level detected by the reproduced level detecting circuit 4 is equal to a reference level. These operations are shown by steps h, i, and j of the flowchart of FIG. 2.
According to the conventional magnetic recording and reproducing circuit as described above, the bias current, the recording level and the recording equalization characteristic can be set to respective optimum values. However, since the oscillation frequency of the low-frequency oscillator 2 for detecting reference recording/reproducing signals is fixed, it is impossible for the recording head to operate under a bias current other than the optimum bias current set using the fixed low frequency. Therefore, while the frequency response can be made flat by the compensation of the bias current, it is difficult to keep a balance of MOLs (maximum output levels) between a middle- and low-frequency range and a high-frequency range.